Re: blktests block/019 lead system hang

[<Austin.Bolen@dell.com>]

On 6/13/2018 10:41 AM, Keith Busch wrote:=0A=
> Thanks for the feedback!=0A=
> This test does indeed toggle the Link Control Link Disable bit to simulat=
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> the link failure. The PCIe specification specifically covers this case=0A=
> in Section 3.2.1, Data Link Control and Management State Machine Rules:=
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>   If the Link Disable bit has been Set by software, then the subsequent=
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>   transition to DL_Inactive must not be considered an error.=0A=
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> So this test should suppress any Suprise Down Error events, but handling=
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> that particular event wasn't the intent of the test (and as you mentioned=
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> it ought not occur anyway since the slot is HP Surprise capable).=0A=
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> The test should not suppress reporting the Data Link Layer State Changed=
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> slot status. And while this doesn't trigger a Slot PDC status, triggering=
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> a DLLSC should occur since the Link Status DLLLA should go to 0 when=0A=
> state machine goes from DL_Active to DL_Down, regardless of if a Suprise=
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> Down Error was detected.=0A=
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> The Linux PCIEHP driver handles a DLLSC link-down event the same as=0A=
> a presence detect remove event, and that's part of what this test was=0A=
> trying to cover.=0A=
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Yes, the R730 could mask the error if OS sets Data Link Layer State=0A=
Changed Enable =3D 1 and could let the OS handle the hot-plug event=0A=
similar to what is done for surprise removal.  Current platform policy=0A=
on R730 is to not do that and only suppress errors related to physical=0A=
surprise removal (PDS =3D 0).  We'll probably forgo the option of=0A=
suppressing any non-surprise remove link down errors even if OS sets=0A=
Data Link Layer State Changed Enable =3D 1 and go straight to the=0A=
containment error recovery model for DPC once the architecture is=0A=
finalized to handle these non-surprise remove related error.  In the=0A=
meantime, it is expected (though not ideal) that this family of servers=0A=
will crash for this particular test.  Ditto for the test that disables=0A=
Memory Space Enable bit in the command register.=0A=
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-Austin=0A=
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